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  <title>Qt 4.3: Customizing Qt Widgets Using Style Sheets</title>
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<h1 align="center">Customizing Qt Widgets Using Style Sheets<br /><small></small></h1>
<p>When using style sheets, every widget is treated as a box with four concentric rectangles: the margin rectangle, the border rectangle, the padding rectangle, and the content rectangle. The box model describes this in further detail.</p>
<a name="box-model"></a><a name="the-box-model"></a>
<h2>The Box Model</h2>
<p>The four concentric rectangles appear conceptually as below:</p>
<p align="center"><img src="images/stylesheet-boxmodel.png" /></p><ul>
<li>The margin falls outside the border.</li>
<li>The border is drawn between the margin and the padding.</li>
<li>The padding falls inside the border, between the border and the actual contents.</li>
<li>The content is what is left from the original widget or subcontrol once we have removed the margin, the border, and the padding.</li>
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<p>The <a href="stylesheet-reference.html#margin-prop">margin</a>, <a href="stylesheet-reference.html#border-width-prop">border-width</a>, and <a href="stylesheet-reference.html#padding-prop">padding</a> properties all default to zero. In that case, all four rectangles (<tt>margin</tt>, <tt>border</tt>, <tt>padding</tt>, and <tt>content</tt>) coincide exactly.</p>
<p>You can specify a background for the widget using the <a href="stylesheet-reference.html#background-image-prop">background-image</a> property. By default, the background-image is drawn only for the area inside the border. This can be changed using the <a href="stylesheet-reference.html#background-clip-prop">background-clip</a> property. You can use <a href="stylesheet-reference.html#background-repeat-prop">background-repeat</a> and <a href="stylesheet-reference.html#background-origin-prop">background-origin</a> to control the repetition and origin of the background image.</p>
<p>A background-image does not scale with the size of the widget. To provide a &quot;skin&quot; or background that scales along with the widget size, one must you the <a href="stylesheet-reference.html#border-image-prop">border-image</a>. Since the border-image property provides an alternate background, it is not required to specify a background-image when border-image is specified. In the case, when both of them are specified, the border-image draws over the background-image.</p>
<p>In addition, the <a href="stylesheet-reference.html#image-prop">image</a> property may be used to draw an image over the border-image. The image specified does not tile or stretch and when its size does not match the size of the widget, it's alignment is specified using the <a href="stylesheet-reference.html#image-position-prop">image-position</a> property. Unlike background-image and border-image, one may specify a SVG in the image property, in which case the image is scaled automatically according to the widget size.</p>
<p>The steps to render a rule are as follows:</p>
<ul>
<li>Set clip for entire rendering operation (border-radius)</li>
<li>Draw the background (background-image)</li>
<li>Draw the border (border-image, border)</li>
<li>Draw overlay image (image)</li>
</ul>
<a name="sub-controls"></a><a name="sub-controls"></a>
<h2>Sub-controls</h2>
<p>A widget is considered as a heirarchy (tree) of subcontrols drawn on top of each other. For example, the <a href="qcombobox.html">QComboBox</a> draws the drop-down sub-control followed by the down-arrow sub-control. A <a href="qcombobox.html">QComboBox</a> is thus rendered as follows:</p>
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<li>Render the <a href="qcombobox.html">QComboBox</a> { } rule</li>
<li>Render the QComboBox::drop-down { } rule</li>
<li>Render the QComboBox::down-arrow { } rule</li>
</ul>
<p>Sub-controls share a parent-child relationship. In the case of <a href="qcombobox.html">QComboBox</a>, the parent of down-arrow is the drop-down and the parent of drop-down is the widget itself. Sub-controls are positioned within their parent using the <a href="stylesheet-reference.html#subcontrol-position-prop">subcontrol-position</a> and <a href="stylesheet-reference.html#subcontrol-origin-prop">subcontrol-origin</a> properties.</p>
<p>Once positioned, sub-controls can be styled using the the <a href="#box-model">box model</a>.</p>
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